How do I ensure that mail-flow is maintained between migrated and un-migrated mailboxes in an Inter- (NETIQKB3658)

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How do I ensure that mail-flow is maintained between migrated and un-migrated mailboxes in an Inter-Organization migration scenario?

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Exchange Migrator 1.x

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Exchange Migrator 2.x

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1. First verify that mail flow works without involving migrated mailboxes.
1. Create a mailbox in the source organization.
2. Create a mailbox in the target organizatoin
3. Send email between the two accounts.
• If this does not work,please consult the Exchange Server's online help or Microsoft Knowledge Base for assistance before migrating with Exchange Migrator.
2. After verifying that native mail flow works, use the EMCLI DIRSYNC command to create Contacts (for Exchange 2000 targets) or Custom Recipients (for Exchange 5.5 targets). These custom recipients will represent the source mailboxes so that newly created target mailboxes, or mailboxes that are created as a result of migration, will be able to select the source mailboxes from the GAL.
3. Migrate mailboxes. If you accept the default settings when you migrate a mailbox in this scenario, Exchange Migrator will create a new mailbox, hide the source mailbox, and create a Custom Recipient on the source Organization for the migrated mailbox. This Custom Recipient is created to receive mail in place of the source mailbox and forward it to the target mailbox.
• When you use the option to "Hide the source mailboxes from the source global address list" in the "Step 3: Specify Migration Options" wizard, Exchange Migrator will automatically hide the source mailbox from the source global address list (GAL) during the mailbox migration.
• You do have the option NOT to "Hide the source mailboxes from the source global address list" and NOT to "Create Custom Recipients in the source when migrating objects" by simply not choosing them.  But, mail-flow between the Organizations will NOT be maintained for the migrated objects.  You might consider NOT choosing these options if you have a short migration that will be completed in a weekend or when no coexistence time period is required during the migration. If you do NOT choose to "Hide the source mailboxes from the source global address list", and instead choose to create a source custom recipient, then the source GAL will have two entries for the same person.  This combination of options is not recommended since it will most likely confuse end-users who attempt to send e-mail via the GAL.
• By default, Exchange Migrator will create a source custom recipient that is configured to forward messages intended for the source mailbox to the newly migrated mailbox on the target.  Exchange Migrator copies all e-mail addresses from the source mailbox's e-mail addresses tab to the source custom recipient's e-mail addresses tab. 
• To resolve e-mail address conflicts between the source hidden mailbox and the source custom recipient created by Exchange Migrator, the text "--migrated--" is added as a prefix to the source mailbox's e-mail addresses.  The additional text also allows you to maintain correct mail-flow after the source Exchange Organization has been decommissioned.  Exchange Migrator removes the prefixed text on the e-mail addresses if you undo the migration.

When e-mail is sent to the source mailbox using secondary e-mail protocols (i.e. not SMTP), such as when an un-migrated mailboxA replies to a message sent from the source un-migrated mailboxB after mailboxB has already been migrated, e-mail is routed to the source mailbox based on an object GUID.  To correctly forward e-mail in these instances, Exchange Migrator modifies the Alt-Recipient property of the source hidden mailbox to forward mail to the source custom recipient, which in turn forwards the e-mail correctly to the target migrated mailbox.  Please reference NETIQ.
KB864 : How are Reply-to messages changed to point to the newly created DN on the target mailbox? for the scenario where migrated mailboxB replies to an e-mail that was sent from mailboxA prior to the migration of mailboxB. The following example may help clarify what has just been stated.

Microsoft Exchange Inter-Organization (Org to Org) migration Scenario

1. Create MB1 and MB2
2. Send email from MB2 to MB1
3. Migrate MB2 while hiding the source mailbox and creating a source CR
4. Log on to MB1 and reply to the email sent by MB2.

What happens at this point?
The email should go to the source hidden mailbox based on an object GUID that is embedded in the email that was originally sent by MB2.  This will then be forwarded to the source CR that was created during the migration process based on the alternate recipient in the source hidden mailbox.  The source CR will then forward the email appropriately to the target mailbox based on SMTP routing.

If you choose the option to "Keep source e-mail addresses" on migrated mailboxes without also translating your source e-mail addresses for the migrated accounts, Exchange Migrator adds a randomly-generated address to the migrated mailbox (Please reference NETIQKB2192 : Why is the SMTP address on the source Custom Recipient garbled after migrating a mailbox? for more information). Adding a randomly-generated address ensures messages are correctly forwarded from the source custom recipient to the target migrated mailbox. You may notice this additional randomly generated e-mail address on your migrated objects.

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Please also reference Message Handling, Reply-to-Addresses, and the Migration Scenarios available in the Exchange Migrator product user guide for additional information.

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Please note that this information can also be obtained from Chapter 3 of the product User Guide.

Formerly known as NETIQKB3658